Facebook appears to be on the back foot. Within 48 hours, the 750m-user site has unveiled two new features aimed – it is said – squarely at Google+ and Twitter.

The social network on Tuesday launched improved friends lists (seen as a tacit admission that Google+ got it right when it comes to organising your friends) and on Wednesday unveiled the subscribe button, allowing people to follow others without befriending them.

Is Facebook feeling the heat? Mark Zuckerberg’s head of engineering, Andrew “Boz” Bosworth, was in London on Friday so we asked the question. (We did have an Audioboo recording of this but apparently the Android app on Samsung Galaxy S phones is more than a little borked. Apologies for that.)

“People, especially with Google+, have been saying, ‘did you launch that in response that?’ and it’s fun to tell that story – from the outside it looks like a cause and effect – but the timelines are a little bit longer than that unfortunately,” he said.

He added that subscriptions had been in “active development” for several months, but “bouncing around” for two years.

So is Facebook (which has roughly one engineer per 1m users) too slow? “We are constantly feeling the pressure. We constantly feel like we’re moving too slowly,” Bosworth admitted. “You can get lots of engineers, but do they dilute the culture? Do they understand the culture? Do they help push you forward? You want every team to be one man short, because that way everyone is at 100%.”

Safe to say, Facebook is in a state of lockdown. The company’s annual developer conference, f8, is less than a week away now – my colleague Stuart Dredge will be attending and we will also be covering it from London – and it promises to be one of the biggest yet. How could Facebook face down its rivals? Think Open Graph, writ huge.